1. Field of the Invention
The present invention relates to a dielectric ceramic composition having a resistance to reduction and to a multi-layer ceramic capacitor or other electronic device using the same.
2. Description of the Related Art
A multi-layer ceramic capacitor, one type of electronic device, is broadly used as a compact, large capacity, high reliability electronic device. The number used in each piece of electronic equipment has also increased. In recent years, along with increasing miniaturization and improved equipment performance, there has been increasingly stronger demand for further reductions in size, increases in capacity, reductions in price and improvements in reliability in multi-layer ceramic capacitors.
Multi-layer ceramic capacitors are normally produced by stacking a paste for forming the internal electrode layers and a paste for forming the dielectric layers using the sheet method or printing method, etc. and then co-firing the internal electrode layers and dielectric layers in the stack together.
As the electroconductive material for the internal electrode layers, generally Pd or a Pd alloy is used, but since Pd is high in price, relatively inexpensive Ni, Ni alloys, and other base metals have come into use. When using a base metal as the electroconductive material of the internal electrode layers, firing in the atmosphere ends up oxidizing the internal electrode layers and therefore the co-firing of the dielectric layers and internal electrode layers has to be done in a reducing atmosphere. When being fired in a reducing atmosphere, however, the dielectric layers end up being reduced and becoming lower in specific resistance. Therefore, non-reducing type dielectric materials are being developed.
In multi-layer ceramic capacitors using a dielectric ceramic composition, insulation resistence (IR) remarkably deteriorates when an electric field is applied, more specifically, there is a disadvantage in that an IR lifetime is short and the credibility is low.
There also arises a disadvantage that when the dielectric composition is exposed to a direct-current electric field, a permittivity ∈r declines over time. Also, a superimposed direct-current voltage is used for a capacitor in some cases and there is a disadvantage that when a direct-current voltage is applied to a capacitor having a dielectric composition wherein a strong dielectric composition is a main composition, a capacitor value generally declines (DC bias characteristics). When a dielectric composition layer is made thinner in order to make a chip capacitor more compact and larger in capacity, an electric field affecting the dielectric composition layer at the time of applying a direct-current voltage becomes strong, so the permittivity ∈r is liable to change over time, that is, the capacitor change over time becomes remarkably large and DC bias characteristics declines.
Further, a capacitor is also required to have excellent temperature characteristics. In particular, in some applications, it is desired that the temperature characteristics be smooth under harsh conditions. In recent years, multi-layer ceramic capacitors have come into use for various types of electronic equipments such as the engine electronic control units (ECU) mounted in engine compartments of automobiles, crank angle sensors, antilock brake system (ABS) modules, etc. These types of electronic equipment are used for stabilizing engine control, drive control, and brake control, and therefore are required to have excellent circuit temperature stability.
The environment in which these types of electronic equipment are used is envisioned to be one in which the temperature falls to as low as xe2x88x9220xc2x0 C. or so in the winter in cold areas or the temperature rises to as high as +130xc2x0 C. or so in the summer right after engine startup. Recently, there has been a trend toward reduction of the number of wire harnesses used for connecting electronic apparatuses and the equipment they control. Electronic apparatuses are also being mounted outside of the vehicles in some cases. Therefore, the environment is becoming increasingly severe for electronic apparatuses. Accordingly, capacitors used for these electronic apparatuses have to have smooth temperature characteristics over a broad temperature range.
Temperature-compensating capacitor materials superior in temperature characteristics such as, (Sr, Ca)(Ti, Zr)O3 based, Ca(Ti, Zr)O3 based, Nd2O3xe2x80x942TiO2 based, La2O3xe2x80x942TiO2 based, and other materials are generally known, but these compositions have extremely low permittivitys (generally less than 100), so it is substantially impossible to produce a capacitor having a large capacity.
To create dielectric ceramic compositions having a high dielectric constant and a smooth capacity-temperature characteristics, compositions comprised of BaTiO3 as a main component plus Nb2O5xe2x80x94Co3O4, MgOxe2x80x94Y, rare earth elements (Dy, Ho, etc.), Bi2O3xe2x80x94TiO2, etc. are known. Looking at the temperature characteristics of a dielectric ceramic composition comprising BaTiO3 as a main component, where the Curie temperature of pure BaTiO3 is close to about 130xc2x0 C., it is extremely difficult to satisfy the R characteristic of the capacity-temperature characteristic (xcex94C=+15% or less) in the region higher in temperature than that. Therefore, a BaTiO3 based high dielectric constant material can only satisfy the X7R characteristic of the EIA standard (xe2x88x9255 to 125xc2x0 C., xcex94C=+15% or less). By only satisfying the X7R characteristic, the material is not good enough to be used in an electronic apparatus of an automobile which is used in the above-mentioned harsh environments. The above electronic apparatus requires a dielectric ceramic composition satisfying the X8R characteristic of the EIA standard (xe2x88x9255 to 150xc2x0 C., xcex94C=xc2x115% or less).
To satisfy the X8R characteristic in a dielectric ceramic composition comprised of BaTiO3 as a main component, it has been proposed to shift the Curie temperature to the high temperature side by replacing the Ba in the BaTiO3 with Bi, Pb, etc. (Japanese Unexamined Patent Publication (Kokai) No. 1998-25157 and No. 1997-40465). Further, it has also been proposed to satisfy the X8R characteristic by selecting a BaTiO3+CaZrO3+ZnO+Nb2O5 based composition (Japanese Unexamined Patent Publication (Kokai) No. 1992-295048, No. 1992-292458, No. 1992-292459, No. 1993-109319, and No. 1994-243721).
In each of these compositions, however, Pb, Bi, and Zn are easily vaporized and scattered making, firing in air or another oxidizing atmosphere a prerequisite. Therefore, there are the problems that it is not possible to use an inexpensive base metal such as Ni for the internal electrodes of the capacitor and it is necessary to use Pd, Au, Ag, or another high priced precious metals.
An object of the present invention is to provide a dielectric ceramic composition having a high permittivity, having a capacity-temperature characteristic satisfying the X8R characteristic of the EIA standard (xe2x88x9255 to 150xc2x0 C., xcex94C=+15% or less), able to be fired in a reducing atmosphere, and further, to provide a multi-layer ceramic capacitor or other electronic device using this dielectric ceramic composition.
To attain the above object, a dielectric ceramic composition according to the first aspect of the present invention comprises:
a main component composed mainly of barium titanate,
a first subcomponent including at least one compound selected from MgO, CaO, BaO, SrO and Cr2O3,
a second subcomponent containing silicone oxide as a main composition,
a third subcomponent including at least one compound selected from V2O, MoO3, and WO3,
a fourth subcomponent including an oxide of R1 (where R1 is at least one element selected from Sc, Er, Tm, Yb, and Lu), and
a fifth subcomponent including CaZrO3 or CaO+ZrO2,
wherein the ratios of the subcomponents to 100 moles of the main component composed mainly of barium titanate are:
the first subcomponent: 0.1 to 3 moles,
the second subcomponent: 2 to 10 moles,
the third subcomponent: 0.01 to 0.5 moles,
the fourth subcomponent: 0.5 to 7 moles (where the number of moles of the fourth subcomponent is the ratio of R1 alone), and
the fifth subcomponent: 0 less than fifth subcomponentxe2x89xa65 moles.
Preferably, in the dielectric ceramic composition according to the present invention, when the number of moles of the fourth subcomponent and the fifth subcomponent with respect to 100 moles of the main component composed mainly of barium titanate (note that the mole number of the fourth subcomponent is the ratio of R1 alone) is expressed by X, Y coordinates, the number of moles of the fourth subcomponent and the fifth subcomponent have the relationship of being within the range surrounded by straight lines of Y=5, Y=0, Y=(2/3)Xxe2x88x92(7/3), X=0.5 and X=5 (where the boundary of Y=0 is not included).
Preferably, in the dielectric ceramic composition according to the present invention, when the number of moles of the fourth subcomponent and the fifth subcomponent with respect to 100 moles of the main component composed mainly of barium titanate (where the mole number of the fourth subcomponent is the ratio of R1 alone) is expressed by X, Y coordinates, the number of moles of the fourth subcomponent and the fifth subcomponent have the relationship of being within the range surrounded by straight lines of Y=5, Y=0, Y=(2/3)Xxe2x88x92(7/3), Y=xe2x88x92(1.5)X+9.5, X=1 and X=5 (where the boundary of Y=0 is not included and boundaries other than Y=0 are included).
Preferably, the dielectric ceramic composition according to the present invention, further comprising a sixth subcomponent an oxide of R2 (where the R2 is at least one element selected from Y, Dy, Ho, Tb, Gd and Eu) and an amount of said sixth subcomponent is not more than 9 moles with respect to 100 moles of the main component composed mainly of barium titanate (where the mole number of the sixth subcomponent is the ratio of R2 alone).
Preferably, a total amount of the fourth subcomponent and the sixth subcomponent is not more than 13 moles with respect to 100 moles of main component composed mainly of barium titanate (where the mole numbers of the fourth subcomponent and sixth subcomponent are respectively the ratios of R1 and R2 alone), more preferably, not more than 10 moles.
Preferably, said second subcomponent is at least one compound selected from SiO2, MO (where M is at least one element selected from Ba, Ca, Sr and Mg), Li2O and B2O3.
More preferably, said second subcomponent is expressed by (Ba, Ca)xSiO2+x(note x=0.7 to 1.2). The second subcomponent is considered to function as a sintering promotion agent.
In the above fifth subcomponent, the mole ratio of Ca and Zr can be any, but preferably, Ca/Zr=0.5 to 1.5, more preferably, Ca/Zr=0.8 to 1.5, furthermore preferably, Ca/Zr=0.9 to 1.1.
Preferably, the dielectric ceramic composition according to the present invention, further comprising a seventh subcomponent MnO, the amount of the seventh subcomponent being not more than 0.5 moles with respect to 100 moles of the main component composed mainly of barium titanate.
To attain the above object, a dielectric ceramic composition according to a second aspect of the present invention comprises:
a main component composed mainly of barium titanate, wherein
when a value of a heat flow difference (dq/dt) per an unit time measured by the DSC (differential scan calorimetry), which is differentiated by a temperature, is defined as a DDSC (Differential Calorimetry Differentiated by Temperature), a temperature difference between a pair of peaks existing on the both sides of the Curie temperature is not less than 4.1xc2x0 C. in a graph showing the relationship between temperature and the DDSC (Differential Calorimetry Differentiated by Temperature).
Note that in a graph showing the relationship of the temperature and the DDSC (Differential Calorimetry Differentiated by Temperature), in the case where peaks are not clear, a dielectric ceramic composition having a half-width of 4.1xc2x0 C. or more in the graph corresponds to that according to the second aspect of the present invention. The half value composition assumes a base line of a heat absorbing peak in the graph showing the relationship between temperature and the DDSC (Differential Calorimetry Differentiated by Temperature), and is defined as a temperature difference between two points sandwiching a peak in which the two points form a straight line parallel to the base line and having a width of xc2xd of the width of the base line.
To attain the above object, a dielectric ceramic composition according to a third aspect of the present invention comprises:
a main component composed mainly of barium titanate, wherein:
a pseudo cubic peak including a peak of a (002) crystal surface and a peak of a (200) crystal surface is observed in a range 2xcex8=44xc2x0 to 46xc2x0 in an X-ray diffraction using a Cuxe2x80x94kxcex1 line;
a half-width of said pseudo cubic peak is not less than 0.3xc2x0 at room temperature; and
when determining the intensity of said peak of the (002) crystal surface is I(002) and the intensity of said peak of the (200) crystal surface is I(200), I(002)xe2x89xa7I(200).
To attain the above object, a dielectric ceramic composition according to a fourth aspect of the present invention comprises:
a main component composed mainly of barium titanate, wherein:
a pseudo cubic peak including a peak of a (004) crystal surface and a peak of a (400) crystal surface is observed in a range 2xcex8=98xc2x0 to 103xc2x0 in an X-ray diffraction using a Cuxe2x80x94Kxcex1 line; and
a half-width of said pseudo cubic peak is not less than 0.4xc2x0 at 120xc2x0 C.
To attain the above object, a dielectric ceramic composition according to a fifth aspect of the present invention comprises:
a main component composed mainly of barium titanate, wherein:
when the dielectric ceramic composition is measured by means of a Raman spectrum method using various sample temperatures, the intensity of the Raman peak at 270 cmxe2x88x921 and 130xc2x0 C. is defined as I270 and the intensity of the Raman peak at 310 cmxe2x88x921 and 130xc2x0 C. is defined as I310, 0.1xe2x89xa6(I310/I270).
To attain the above object, a dielectric ceramic composition according to a sixth aspect of the present invention comprises:
a main component composed mainly of barium titanate, wherein:
when the dielectric ceramic composition is measured by means of a Raman spectrum method using various sample temperatures,
A half-width of the Raman peak at 535 cmxe2x88x921 is not more than 95 cmxe2x88x921 at the sample temperature of 130xc2x0 C.
Preferably, in dielectric ceramic compositions according to the first to sixth aspects, barium titanate is expressed by a composition formula of BamTiO2+m, wherein m in the composition formula is 0.995xe2x89xa6mxe2x89xa61.010, and the ratio of Ba and Ti is 0.995xe2x89xa6Ba/Tixe2x89xa61.010.
An electric device according to the present invention is not specifically limited as far as it includes a dielectric layer, and for example a multi-layer ceramic capacitor device having a capacitor device body wherein dielectric layers and internal electrode layers are alternately layered. In the present invention, the dielectric layer is composed of any of the above dielectric ceramic compositions. A conductive material included in the internal electrode layer is not specifically limited, but is for example Ni or a Ni alloy.
A dielectric ceramic composition according to the present invention has a high permittivity, satisfying the X8R characteristic of the EIA standard (xe2x88x9255 to 150xc2x0 C., xcex94C=xc2x115% or less), and is able to be fired in a reducing atmosphere, and further, has a small change of capacity over time when under a direct-current electric field.
Also, a dielectric ceramic composition according to the present invention has a long insulation resistence life, furthermore, DC bias characteristics (direct-current voltage application dependency of the dielectric constant) and TC bias characteristics (capacity-temperature characteristics at the time of direct-current application) are stable.
Accordingly, by using the dielectric ceramic composition of the present invention, it becomes eaier to provide an interlayer ceramic capacitor and other electric devices having excellent characteristics.
Namely, since interlayer ceramic capacitors and other electric devices having a dielectric composition layer comprised of the dielectric ceramic composition of the present invention are able to stably operate in a variety of apparatuses used under hard circumstances, such as electric apparatuses in vehicles, the credibility of those apparatuses to which the same is applied is remarkably improved.
Furthermore, the temperature characteristics of a ceramic composition of an X8R characteristic material of the related art is liable to be deteriorated by making the film thinner, and the X7R characteristics cannot be satisfied particularly when an interlayer is not more than 5 xcexcm in some cases. On the contrary, the present invention is also effective in improving the temperature characteristics in the case of such thinner films.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 1999-297269 (filed on October 19) and No. 2000-226862 (filed on July 27), the disclosure of which is expressly incorporated herein by reference in its entirety.